Effects of fermentation on the structural characteristics and in vitro binding capacity of soluble dietary fiber from tea residues

The effects of Trichoderma viride fermentation treatment on the structural characteristics and in vitro binding capacity of three heavy metal ions (Pb, Cd, Cu) of soluble dietary fiber (SDF) from tea residues were investigated. Compared with the yield of SDF from untreated tea residues (U-SDF), that of fermented tea residues (F-SDF) significantly increased from 4.3% to 31.56% under the optimal conditions by using response surface methodology. The F-SDF exhibited higher uronic acid content (34.82% vs 17.81%), crystallinity (23.11% vs 17.36%) and thermal stability than U-SDF. Moreover, the specific surface area of F-SDF increased after fermentation by SEM analysis. Difference appeared in the monosaccharide composition ratio of F-SDF (0.06:0.77:1.00:2.41:0.63:0.86:1.80) and U-SDF (0.02:0.81:1.00:0.34:0.13:1.39). Furthermore, the binding capacity of SDF for Pb, Cd, and Cu at pH 7.0 were more than 2.4 times than that at pH 2.0. The binding capacity of F-SDF for Pb (664.5 vs 590.7 μmol/g), Cd (405.6 vs 349.6 μmol/g), and Cu (368.5 vs 307.9 μmol/g) were significantly increased than U-SDF. The overall results indicated that F-SDF could be used as a potential food additive to protect the body from the hazard of food-derived heavy metals.